This invention relates generally to nickel-hydrogen (Ni/H.sub.2) storage batteries and, more particularly, to a process for producing nickel electrodes having desirable utilization characteristics.
Nickel-hydrogen batteries became a major workhorse for many spacecraft, especially in geosynchronous earth orbit, because of their high reliability and long calendar and cycle life. Mission duration of some satellites has been extended beyond fifteen years as the reliability of other components of the spacecraft improved.
The nickel-hydrogen cell includes a cell stack which is made of a series of active plate sets, each plate set having a nickel hydroxide/oxide positive electrode (termed a "nickel electrode"), a hydrogen negative electrode, a separator between the electrodes, and an electrolyte such as an aqueous solution of potassium hydroxide. The nickel electrode is manufactured by impregnating a porous nickel substrate with nickel hydroxide active material which is reversibly converted to nickel oxyhydroxide in the cell when it is charged. The cell stack is packaged within a pressure vessel in which hydrogen gas is evolved and consumed when the cell is charged and discharged. A nickel-hydrogen storage cell has an open circuit voltage of about 1.3 volts, and a number of the cells are usually connected in series to provide the voltage required by the spacecraft power system. The charge capacity of the power system is adjusted by the total area of electrode in the cell.
The battery is one of the major weight components of many devices such as spacecraft and many other electronic devices, especially as their power demand is being increased. The nickel electrode is the heaviest component of presently used nickel-hydrogen cells, accounting for about one-third or more of the cell weight. The weight of the sintered-type nickel substrate is approximately 60% of the weight of the nickel electrode. Therefore, use of a lightweight, high porosity nickel substrate for the nickel electrode is very attractive. For example, use of a 90% porous substrate which weighs only one-half of a presently used 80% porous substrate will reduce the nickel electrode weight substantially (approximately by 30%) if the active material is fully utilized. The higher the porosity, the lighter the substrate weight becomes. In general, however, the higher the porosity, the poorer the utilization of the active material becomes.
Therefore, a principal object of the present invention is to provide a manufacturing process for a nickel electrode using a high porosity, lightweight substrate with the maximum utilization of the active material.
Other objects and advantages of the present invention will become apparent from the following detailed disclosure and description.